Copending application Ser. No. 300,046, filed Sept. 8, 1981, in the name of Thomas J. Walter--Walter I--discloses 4-(3-chlorocyclohex-3-enyl)pyridine, 4-(4-chlorocyclohex-3-enyl)pyridine, a process for making these compounds by a Diels-Alder reaction between chloroprene and a 4-vinylpyridine, and a process for converting them to 4-(3-chlorophenyl)pyridine and 4-(4-chlorophenyl)pyridine by catalytic dehydrogenation.
Copending application Ser. No. 495,977, filed May 19, 1983, in the name of Thomas J. Walter--Walter II--discloses processes by which 4-(4-halophenyl)pyridines, such as the 4-(4-chlorophenyl)pyridine produced in Walter I, can be converted to 4-(4-halo-3-nitrophenyl)pyridines, then to 4-(3-aminophenyl)pyridines, and ultimately to the antibacterial 1-alkyl-1,4-dihydro-4-oxo-7-pyridinyl-3-quinolinecarboxylic acids of Sterling Drug's U.S. Pat. No. 3,753,993 (Lesher et al.), U.S. Pat. No. 3,907,808 (Lesher and Carabateas), and U.S. Pat. No. 4,118,557 (Lesher).
Copending application Ser. No. 497,026, filed May 23, 1983, in the name of V. Ramachandran--Ramachandran--discloses improved processes for preparing the 4-(halocyclohex-3-enyl)pyridines and derivatives wherein a boron trifluoride catalyst is employed directly to improve the yield of 4-(halocyclohex-3-enyl)pyridine and indirectly to improve the yields of derivatives thereof.
Separately and in combination, the aforementioned copending applications disclose useful processes for preparing antibacterial agents and intermediates thereof. However, since the products of the Diels-Alder reactions of these applications, i.e., the 4-(halocyclohex-3-enyl)pyridine mixtures, are not easily separated from one another and/or reduced, there is still room for improvements in these processes.